SPF Fail: Common Causes and How to Fix Them

Let us walk you through the many causes of SPF Fail. This article will review the types of failures and explain best practices to avoid future SPF Failures.

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SPF Fail: Common Causes and How to Fix Them
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Sender Policy Framework, or SPF, is one of the email authentication protocols organizations have used in their email systems for years to reduce spam and authorize sending sources. However, it is common to run into different errors that result in SPF Failure. In this post, we discuss what can cause SPF to fail, and how to fix it.

Here are some common reasons leading to SPF failures: 

  • SPF record syntax errors 
  • SPF record configuration errors 
  • Exceeding DNS lookup limits for SPF
  • Forwarding emails 
  • Incomplete sending source authorization

Why Do SPF Failures Happen? 

SPF failures can occur due to the following reasons:

  • The receiving MTA fails to find an SPF record published in your DNS.
  • You have configured more than one SPF record for the same domain. 
  • Your email service providers have modified or added new IP addresses that you haven’t included in your SPF record.
  • You have surpassed the 10 DNS lookup limit for SPF.
  • You are exceeding the maximum number of permitted void lookup limit of 2.
  • Your flattened SPF record length exceeds the 255 SPF characters limit.

When SPF fails for your email, your next steps should be to identify the reason behind it so you can resolve it. This is possible through regular monitoring of DMARC reports. PowerDMARC helps you read reports on SPF authentication failures easily with our DMARC analyzer.

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Types of SPF Failures

The following are types of SPF fail qualifiers each of which is added as a prefix before the SPF mechanism:

“+” “Pass”
“-” “Fail”
“~” “Softfail”
“?” “Neutral”

How do these matter? Well in a situation where your email is rejected, you can choose how stringently you want receivers to handle it. You may specify a qualifier to “pass” messages that have received an SPF “Fail” delivery, or take a “Neutral” standpoint (do nothing).

1. SPF None Result Returned

In the first case scenario, if the receiving email server performs a DNS lookup and is unable to find the domain name in the DNS, a none result is returned. None is also returned in case no SPF record is found in the sender’s DNS, which implies that the sender doesn’t have SPF authentication configured for this domain. In this case, SPF authentication for your emails fails, which is denoted by “-all”.

Generate your error-free SPF record now with our free SPF record generator tool to avoid this.

2. SPF Neutral Result Returned

While configuring SPF for your domain, if you have affixed an “?all” mechanism to your SPF record, this means that no matter what the SPF authentication checks for your outbound emails conclude, the receiving MTA returns a neutral result. This happens because when you have your SPF in neutral mode, you are not specifying the IP addresses that are authorized to send emails on your behalf and allowing unauthorized IP addresses to send them as well.

3. SPF Softfail Result Returned

Similar to SPF neutral, SPF softfail is identified by ~all mechanism which implies that the receiving MTA would accept the mail and deliver it into the inbox of the recipient, but it would be marked as spam, in case the IP address is not listed in the SPF record found in the DNS, which can be a reason why SPF authentication fails for your email. Given below is an example of SPF softfail:

 v=spf1 include:spf.google.com ~all

4. SPF Hardfail Result Returned

SPF hardfail is when receiving MTAs discard emails originating from any sending source that is not listed within your SPF record. We recommend you to configure SPF hardfail in your SPF record if you want to gain protection against domain impersonation and email spoofing. 

Example: v=spf1 include:spf.google.com -all

Learn the specific difference of  SPF softfail vs hardfail

5. SPF Temperror (SPF Temporary Error)

One common and often harmless reasons why SPF authentication fails is SPF Temperror (temporary error). This is caused by a DNS error such as a DNS timeout. It is, therefore, just as the name suggests, an interim error returning a 4xx status code that can cause a temporary SPF failure. It will yield an SPF pass result when tried again later.

6. SPF Permerror (SPF Permanent Error)

Another common error that domains face is an SPF Permerror. This is when there is a failure with a permanent error. This happens when your SPF record gets invalidated by the receiving MTA. There are many reasons why SPF might break and be rendered invalid by the MTA while performing DNS lookups:

  • Exceeding the 10 SPF lookup limit
  • Incorrect SPF record syntax
  • More than one SPF record for the same domain
  • Exceeding the SPF record length limit of 255 characters
  • If your SPF record is not up to date with changes made by your ESPs

Note: When an MTA performs an SPF check on an email, it queries the DNS or conducts a DNS lookup to check for the authenticity of the email source. Ideally, in SPF you are allowed a maximum of 10 DNS lookups, exceeding which will cause SPF to break and return a Permerror result. This is a very common issue leading to SPF fail. 

How to Fix An SPF Fail for Emails

For smooth deliverability, it is important to ensure SPF doesn’t fail for your emails. To fix SPF fails, you can follow these best practices: 

1. Stay within SPF Limits

If your authentication fails because of DNS lookups exceeding RFC-specified limits, try to stay within the limit to prevent the failure. PowerDMARC helps customers optimize their SPF records to stay under these hard limits through Macros. Often, they are several times more effective than SPF flattening, Macros in your SPF DNS record help you avoid exceeding DNS void and lookup limits at all times. 

2. Avoid Syntax and Configuration Errors

Manually implementing SPF records often leads to syntax errors and causes them to fail. To ensure you are using the right syntax for SPF, generate your record with the help of an automated SPF record generator tool.

When configuring SPF in your DNS, always use the resource type “TXT”. If you configure the wrong resource type like “CNAME” or even “SPF”, it will lead to configuration errors and an SPF failure. 

3. Authorize All Sending Sources

Make sure you are properly authorizing all your sending sources including your third-party vendors, in your SPF record. Your vendors often change or add to their list of sending IPs. You must make sure you are on top of such changes and implement them in your own SPF record. Missing out on authorized sending sources often leads to unwarranted SPF failures. 

4. Combine Multiple SPF Records 

More than one SPF record for the same domain can invalidate your SPF implementation and lead to SPF failure. In such cases, it is better to combine multiple records into a single record by using the “include” mechanism. 

SPF Best Practices

Domain owners abiding by the above-mentioned SPF best practices can significantly reduce the chances of unwarranted SPF fail. Here are some additional good practices that businesses can exercise in general to further strengthen their email security: 

  • Use DKIM to avoid SPF fail for forwarded emails 
  • Use DMARC and DKIM, so that even if SPF fails and DKIM passes, DMARC will pass 
  • Enable DMARC reporting to monitor SPF failures and causes 

Email authentication failures are never good news for your domain’s reputation and credibility. To ensure your deliverability isn’t affected, you need to take action now to prevent your SPF from failing. Want to test if you have SPF configured correctly for your domain? Try out our free SPF checker tool today!

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